Estimating Practice Exam

Allowable stresses for lumber are specified according to what factor?

1. Type of wood

2. Species

3. Grade

4. Size

The correct answer is: Species

Allowable stresses for lumber are indeed specified according to the species of the wood. Different species have different physical and mechanical properties, which greatly influence how much stress the wood can withstand before failing. For example, denser woods typically can bear more load compared to lighter woods, thus leading to variations in allowable stresses based on species. The grading of lumber is essential as well, as it indicates the quality and structural integrity of the wood, but it is the species that primarily determines the fundamental characteristics that affect stress limits. Factors like growth conditions and the specific anatomical structure of the wood species contribute significantly to its strength properties. While the type of wood may suggest a broader category, the specific species provides more precise information necessary for determining allowable stress values in structural applications. Lastly, size is a consideration in determining bending strengths and load-carrying capacities, but it does not directly influence the allowable stresses which are mainly driven by species.